The word "best" is tricky because it actually defines nothing at all: it doesn't define which point of view you took when you said that object X has the highest quality. If you need speed, ZIP is the "best"; if you need highest compression ratio, probably 7-Zip is the "best"; if you need high compression ratio, high functionality/configurability and being an established de facto standard then RAR is the "best".
ZIP has been around for ages, it's been cleaned out and re-written in the form of free software (Info-Zip); because of its extreme compression speed - almost as fast as simply copying files -, it's ideal for small and/or often rearchived stuff.
RAR is not so old but also has been around for so long that it effectively killed its able competitors: first ARJ and then ACE. Its 2.x DOS versions had a nice Norton-like user interface (yummy!) and the 3.x Windows versions can also be integrated into Windows Explorer. (I don't like GUI's but this is important for the average user.) It has a wide range of compression ratios, from fast & not so good to very slow & squeeze the last bits out. It also has an great amount of configuration options and copies all major functions from ARJ.
I don't know 7-Zip much. Yes, it's free software but it hasn't been around for a long enough to become a de facto standard, unlike ZIP and RAR. One of the reasons for its even higher compression ratio may be using solid archives
by default: this is one of the tricks that ACE used to boast its own compression ratios; if you switched it off manually, it wasn't much better - if at all - than RAR anymore! Another reason could be using different adaptivity for the same compression algorithm or using a completely different algorithm, although RAR itself has a lot of them (e.g. one especially for multimedia files; also see UHArc for such purposes!).
As for archiver comparisons, they're like opinions and assholes: everyone has one and noone is interested in that of others...
